dtl.c

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/*
 * Virtual Processor Dispatch Trace Log
 *
 * (C) Copyright IBM Corporation 2009
 *
 * Author: Jeremy Kerr <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/init.h>
#include <linux/slab.h>
#include <linux/debugfs.h>
#include <linux/spinlock.h>
#include <asm/smp.h>
#include <asm/uaccess.h>
#include <asm/firmware.h>
#include <asm/lppaca.h>
#include <asm/debug.h>

#include "plpar_wrappers.h"

struct dtl {
    struct dtl_entry    *buf;
    struct dentry       *file;
    int         cpu;
    int         buf_entries;
    u64         last_idx;
    spinlock_t      lock;
};
static DEFINE_PER_CPU(struct dtl, cpu_dtl);

/*
 * Dispatch trace log event mask:
 * 0x7: 0x1: voluntary virtual processor waits
 *      0x2: time-slice preempts
 *      0x4: virtual partition memory page faults
 */
static u8 dtl_event_mask = 0x7;


/*
 * Size of per-cpu log buffers. Firmware requires that the buffer does
 * not cross a 4k boundary.
 */
static int dtl_buf_entries = N_DISPATCH_LOG;

#ifdef CONFIG_VIRT_CPU_ACCOUNTING
struct dtl_ring {
    u64 write_index;
    struct dtl_entry *write_ptr;
    struct dtl_entry *buf;
    struct dtl_entry *buf_end;
    u8  saved_dtl_mask;
};

static DEFINE_PER_CPU(struct dtl_ring, dtl_rings);

static atomic_t dtl_count;

/*
 * The cpu accounting code controls the DTL ring buffer, and we get
 * given entries as they are processed.
 */
static void consume_dtle(struct dtl_entry *dtle, u64 index)
{
    struct dtl_ring *dtlr = &__get_cpu_var(dtl_rings);
    struct dtl_entry *wp = dtlr->write_ptr;
    struct lppaca *vpa = local_paca->lppaca_ptr;

    if (!wp)
        return;

    *wp = *dtle;
    barrier();

    /* check for hypervisor ring buffer overflow, ignore this entry if so */
    if (index + N_DISPATCH_LOG < vpa->dtl_idx)
        return;

    ++wp;
    if (wp == dtlr->buf_end)
        wp = dtlr->buf;
    dtlr->write_ptr = wp;

    /* incrementing write_index makes the new entry visible */
    smp_wmb();
    ++dtlr->write_index;
}

static int dtl_start(struct dtl *dtl)
{
    struct dtl_ring *dtlr = &per_cpu(dtl_rings, dtl->cpu);

    dtlr->buf = dtl->buf;
    dtlr->buf_end = dtl->buf + dtl->buf_entries;
    dtlr->write_index = 0;

    /* setting write_ptr enables logging into our buffer */
    smp_wmb();
    dtlr->write_ptr = dtl->buf;

    /* enable event logging */
    dtlr->saved_dtl_mask = lppaca_of(dtl->cpu).dtl_enable_mask;
    lppaca_of(dtl->cpu).dtl_enable_mask |= dtl_event_mask;

    dtl_consumer = consume_dtle;
    atomic_inc(&dtl_count);
    return 0;
}

static void dtl_stop(struct dtl *dtl)
{
    struct dtl_ring *dtlr = &per_cpu(dtl_rings, dtl->cpu);

    dtlr->write_ptr = NULL;
    smp_wmb();

    dtlr->buf = NULL;

    /* restore dtl_enable_mask */
    lppaca_of(dtl->cpu).dtl_enable_mask = dtlr->saved_dtl_mask;

    if (atomic_dec_and_test(&dtl_count))
        dtl_consumer = NULL;
}

static u64 dtl_current_index(struct dtl *dtl)
{
    return per_cpu(dtl_rings, dtl->cpu).write_index;
}

#else /* CONFIG_VIRT_CPU_ACCOUNTING */

static int dtl_start(struct dtl *dtl)
{
    unsigned long addr;
    int ret, hwcpu;

    /* Register our dtl buffer with the hypervisor. The HV expects the
     * buffer size to be passed in the second word of the buffer */
    ((u32 *)dtl->buf)[1] = DISPATCH_LOG_BYTES;

    hwcpu = get_hard_smp_processor_id(dtl->cpu);
    addr = __pa(dtl->buf);
    ret = register_dtl(hwcpu, addr);
    if (ret) {
        printk(KERN_WARNING "%s: DTL registration for cpu %d (hw %d) "
               "failed with %d\n", __func__, dtl->cpu, hwcpu, ret);
        return -EIO;
    }

    /* set our initial buffer indices */
    lppaca_of(dtl->cpu).dtl_idx = 0;

    /* ensure that our updates to the lppaca fields have occurred before
     * we actually enable the logging */
    smp_wmb();

    /* enable event logging */
    lppaca_of(dtl->cpu).dtl_enable_mask = dtl_event_mask;

    return 0;
}

static void dtl_stop(struct dtl *dtl)
{
    int hwcpu = get_hard_smp_processor_id(dtl->cpu);

    lppaca_of(dtl->cpu).dtl_enable_mask = 0x0;

    unregister_dtl(hwcpu);
}

static u64 dtl_current_index(struct dtl *dtl)
{
    return lppaca_of(dtl->cpu).dtl_idx;
}
#endif /* CONFIG_VIRT_CPU_ACCOUNTING */

static int dtl_enable(struct dtl *dtl)
{
    long int n_entries;
    long int rc;
    struct dtl_entry *buf = NULL;

    if (!dtl_cache)
        return -ENOMEM;

    /* only allow one reader */
    if (dtl->buf)
        return -EBUSY;

    n_entries = dtl_buf_entries;
    buf = kmem_cache_alloc_node(dtl_cache, GFP_KERNEL, cpu_to_node(dtl->cpu));
    if (!buf) {
        printk(KERN_WARNING "%s: buffer alloc failed for cpu %d\n",
                __func__, dtl->cpu);
        return -ENOMEM;
    }

    spin_lock(&dtl->lock);
    rc = -EBUSY;
    if (!dtl->buf) {
        /* store the original allocation size for use during read */
        dtl->buf_entries = n_entries;
        dtl->buf = buf;
        dtl->last_idx = 0;
        rc = dtl_start(dtl);
        if (rc)
            dtl->buf = NULL;
    }
    spin_unlock(&dtl->lock);

    if (rc)
        kmem_cache_free(dtl_cache, buf);
    return rc;
}

static void dtl_disable(struct dtl *dtl)
{
    spin_lock(&dtl->lock);
    dtl_stop(dtl);
    kmem_cache_free(dtl_cache, dtl->buf);
    dtl->buf = NULL;
    dtl->buf_entries = 0;
    spin_unlock(&dtl->lock);
}

/* file interface */

static int dtl_file_open(struct inode *inode, struct file *filp)
{
    struct dtl *dtl = inode->i_private;
    int rc;

    rc = dtl_enable(dtl);
    if (rc)
        return rc;

    filp->private_data = dtl;
    return 0;
}

static int dtl_file_release(struct inode *inode, struct file *filp)
{
    struct dtl *dtl = inode->i_private;
    dtl_disable(dtl);
    return 0;
}

static ssize_t dtl_file_read(struct file *filp, char __user *buf, size_t len,
        loff_t *pos)
{
    long int rc, n_read, n_req, read_size;
    struct dtl *dtl;
    u64 cur_idx, last_idx, i;

    if ((len % sizeof(struct dtl_entry)) != 0)
        return -EINVAL;

    dtl = filp->private_data;

    /* requested number of entries to read */
    n_req = len / sizeof(struct dtl_entry);

    /* actual number of entries read */
    n_read = 0;

    spin_lock(&dtl->lock);

    cur_idx = dtl_current_index(dtl);
    last_idx = dtl->last_idx;

    if (last_idx + dtl->buf_entries <= cur_idx)
        last_idx = cur_idx - dtl->buf_entries + 1;

    if (last_idx + n_req > cur_idx)
        n_req = cur_idx - last_idx;

    if (n_req > 0)
        dtl->last_idx = last_idx + n_req;

    spin_unlock(&dtl->lock);

    if (n_req <= 0)
        return 0;

    i = last_idx % dtl->buf_entries;

    /* read the tail of the buffer if we've wrapped */
    if (i + n_req > dtl->buf_entries) {
        read_size = dtl->buf_entries - i;

        rc = copy_to_user(buf, &dtl->buf[i],
                read_size * sizeof(struct dtl_entry));
        if (rc)
            return -EFAULT;

        i = 0;
        n_req -= read_size;
        n_read += read_size;
        buf += read_size * sizeof(struct dtl_entry);
    }

    /* .. and now the head */
    rc = copy_to_user(buf, &dtl->buf[i], n_req * sizeof(struct dtl_entry));
    if (rc)
        return -EFAULT;

    n_read += n_req;

    return n_read * sizeof(struct dtl_entry);
}

static const struct file_operations dtl_fops = {
    .open       = dtl_file_open,
    .release    = dtl_file_release,
    .read       = dtl_file_read,
    .llseek     = no_llseek,
};

static struct dentry *dtl_dir;

static int dtl_setup_file(struct dtl *dtl)
{
    char name[10];

    sprintf(name, "cpu-%d", dtl->cpu);

    dtl->file = debugfs_create_file(name, 0400, dtl_dir, dtl, &dtl_fops);
    if (!dtl->file)
        return -ENOMEM;

    return 0;
}

static int dtl_init(void)
{
    struct dentry *event_mask_file, *buf_entries_file;
    int rc, i;

    if (!firmware_has_feature(FW_FEATURE_SPLPAR))
        return -ENODEV;

    /* set up common debugfs structure */

    rc = -ENOMEM;
    dtl_dir = debugfs_create_dir("dtl", powerpc_debugfs_root);
    if (!dtl_dir) {
        printk(KERN_WARNING "%s: can't create dtl root dir\n",
                __func__);
        goto err;
    }

    event_mask_file = debugfs_create_x8("dtl_event_mask", 0600,
                dtl_dir, &dtl_event_mask);
    buf_entries_file = debugfs_create_u32("dtl_buf_entries", 0400,
                dtl_dir, &dtl_buf_entries);

    if (!event_mask_file || !buf_entries_file) {
        printk(KERN_WARNING "%s: can't create dtl files\n", __func__);
        goto err_remove_dir;
    }

    /* set up the per-cpu log structures */
    for_each_possible_cpu(i) {
        struct dtl *dtl = &per_cpu(cpu_dtl, i);
        spin_lock_init(&dtl->lock);
        dtl->cpu = i;

        rc = dtl_setup_file(dtl);
        if (rc)
            goto err_remove_dir;
    }

    return 0;

err_remove_dir:
    debugfs_remove_recursive(dtl_dir);
err:
    return rc;
}
arch_initcall(dtl_init);